Sabre boxing - sport that usually has four letters (9)
I believe the answer is:
swearword
'sabre boxing sport that usually has four letters' is the definition.
Although both the answer and definition are singular nouns, I don't understand how they can define each other.
'sabre boxing sport' is the wordplay.
'sabre' becomes 'sword' (I can't explain this - if you can you should give a lot more credence to this answer).
'boxing' indicates putting letters inside ('box' can mean contain, as in to put in a box).
'sport' becomes 'wear' (sport can mean to wear or display on one's person).
'sword' going around 'wear' is 'SWEARWORD'.
Can you help me to learn more?
(Other definitions for swearword that I've seen before include "profanity" , "blast perhaps" , "Oath" .)